Conventionally, a memory device is used to store voltage levels representing digital information. It has become necessary for a memory device to process multilevel information because of limitations. Multi-valued computation is difficult for the conventional digital circuit. The inventors of the present invention have proposed a circuit for converting analog voltage into a function of time by an exponential using an RC circuit. In the time domain, multiplication and division of the analog voltage is expressed by an addition and subtraction. It is necessary to hold data for the calculation above, however, there is no such memory means.